This invention relates to hub caps for vehicles which hub caps incorporate grease fittings for injecting grease into wheel bearings and pressure relief structure for releasing grease under pressure without damaging other bearing seals and the like.
A typical use for a hub cap of this type is on a boat trailer where the trailer is submerged in the water during launching and recovery of the boat.
A wheel bearing is packed with grease. When the trailer is being towed, the bearings and grease heat up and the grease expands. Air and grease are forced from the structure. When the hot trailer is immerged in water during launching, there is a sudden cooling and contraction of the grease when tends to create a vacuum and suck water into the bearing area. This is highly undesirable. If the bearing structure is packed full with grease and designed so that no air or grease can escape, another problem arises. When the vehicle is being towed, the grease heats and the pressure within the hub expands with the increased pressure causing damage to the bearing seals which may be on the inner side of the hub so that leaking grease is not immediately noticed with the result that the bearings become dry and freeze.
Several types of pressure relief hub caps have been produced in the past. One type is shown in U.S. Pat. No. 3,785,706 to Van Galis. In this device, a cup shaped seal is mounted within a cup shaped hub cap, with a spring acting on the seal to compress the grease within the hub. A first opening in the cap adjacent the outer end provides for pressure relief in the spring area between the seal and the outer end of the hub cap. A second opening in the hub cap inboard from the first opening provides for escape of grease when the pressure within the hub is sufficient to compress the spring.
Another type of hub cap is shown in U.S. Pat. No. 3,077,948 to Law. This structure utilizes a cup shaped seal sliding in a sleeve with a spring urging the seal inward to compress the grease. The sealing action occurs between the cup shaped seal and an 0-ring in the inner surface of the sleeve. A grease fitting is carried in the sliding seal for introducing grease into the hub.
The hub cap of the U.S. Pat. No. 3,785,706 patent suffers from the disadvantage that grease can be added to the hub only by removing the hub cap. This problem is solved by the hub cap of the U.S. Pat. No. 3,077,948 patent. However there are still some disadvantages with this structure. When the hub is being filled with grease by a grease gun, the manual force utilized in holding the grease gun in place also acts to hold the sliding seal in fixed position so that excess pressure can be built up within the hub and the inner bearing seal can be damaged without the operator knowing of this fact. That is, the automatic pressure release operation is nullified by the force applied with the grease gun. Also, the cup shaped seal which slides within the outer sleeve or housing and engages the 0-ring for making a seal provides only limited area for escape of grease.
Accordingly, it is an object of the present invention to provide a new and improved hub cap for sealing against entrance of moisture while providing automatic release under high pressure. A further object is to provide such a hub cap wherein the automatic pressure release functions at all times, including the period when grease is being introduced into the hug. A further object is to provide a new and improved hub cap with an improved sealing construction which provides for a quick release of relatively high rate of flow of grease and a quick seal. Other objects, advantages, features and results will more fully appear in the course of the following description.